Flash memory devices have developed into a popular source of non-volatile memory for a wide range of electronic applications. Flash memory devices typically use a one-transistor memory cell that allows for high memory densities, high reliability, and low power consumption. Common uses for flash memory include portable computers, personal digital assistants (PDAs), digital cameras, portable music players, and cellular telephones. Program code, system data such as a basic input/output system (BIOS), and other firmware can typically be stored in flash memory devices. Many electronic devices are designed with a single flash memory device.
Two common types of flash memory array architectures are the “NAND” and “NOR” architectures, so called for the resemblance which the basic memory cell configuration of each architecture has to a basic NAND or NOR gate circuit, respectively. In the NOR array architecture, the floating gate memory cells of the memory array are arranged in a matrix. The gates of each floating gate memory cell of the array matrix are connected by rows to word select lines (word lines) and their drains are connected to column bit lines. The source of each floating gate memory cell is typically connected to a common source line. The NOR architecture floating gate memory array is accessed by a row decoder activating a row of floating gate memory cells by selecting the word line connected to their gates. The row of selected memory cells then place their stored data values on the column bit lines by flowing a differing current if in a programmed state, or non-programmed state from the connected source line to the connected column bit lines.
A NAND array architecture also arranges its array of floating gate memory cells in a matrix such that the gates of each floating gate memory cell of the array are connected by rows to word lines. However each memory cell is not directly connected to a source line and a column bit line. Instead, the memory cells of the array are arranged together in strings, typically of 8, 16, 32, or more each, where the memory cells in the string are connected together in series, source to drain, between a common source line and a column bit line. The NAND architecture floating gate memory array is then accessed by a row decoder activating a row of floating gate memory cells by selecting the word select line connected to their gates. In addition, the word lines connected to the gates of the unselected memory cells of each string are also driven. However, the unselected memory cells of each string are typically driven by a higher gate voltage so as to operate them as pass transistors and allowing them to pass current in a manner that is unrestricted by their stored data values. Current then flows from the source line to the column bit line through each floating gate memory cell of the series connected string, restricted only by the memory cells of each string that are selected to be read, thereby placing the current encoded stored data values of the row of selected memory cells on the column bit lines.
NAND flash memory array architectures of the type discussed above are generally known as discussed, for example, in U.S. Pat. Nos. 6,975,538 and 6,977,842, assigned to Micron Technology, Inc., which are hereby incorporated by reference in their entirety.
NAND flash memory devices are being used more and more in consumer electronics due to the potentially high memory densities at relatively low cost. In order to get higher and higher capacities, system designers are putting more and more dies in the same package to get those desired densities. Dual die packages as well as quad die packages increase density, but they also create issues with current consumption and noise. Environmental factors may also increasingly affect operation of memory devices, especially those with high packing densities.
Consumer devices such as those described also have operating modes with which a system designer may be concerned, depending on environmental factors. For instance, a handheld device may have two modes of operation: a first for high performance operation where the device is plugged into an outlet and there is no concern for power depletion, and a second for modes where a battery is used and peak currents and depletion of power are issues.
NAND memories have operating cycles that consume large amounts of current. Such current peaks can be reduced, but the performance of the memory would be adversely impacted. By placing circuits that limit the current in the charging path of some cycles, the maximum current could be controlled. However, it would take longer to pass that amount of current to the node that needs it. Also, as mentioned earlier, the device that is sold to the system designer may include multiple stacked NAND flash memories. In those cases, the peak currents add up and create significant problems for the system. In a system where the die is used in a quad stack, the total peak current gets quadrupled. The system designer may want smaller peak currents which may negatively impact device performance.
Accordingly, there is a need in the art for an improved method and apparatus for managing operation of an integrated circuit device in accordance with environmental influences, such as, for example, the power consumption in a an integrated circuit, for example, memory devices with a flash memory device, being one example of a memory device.